The present disclosure relates to a laser, imaging device and method. More particularly, the present disclosure relates to a laser, imaging device and method utilizing x-ray energy emission from the laser.
It is known to use x-ray photons to create images of interior portions of an object, such as luggage, industrial parts, a human or animal. Computed tomography and laminography are examples of imaging techniques that use broad band ionizing radiation.
There are several disadvantages in medical imaging to using broad band ionizing radiation or photons at many different energy levels. Very high energy levels can decrease the signal-to-noise level by increasing the noise in the images. It has been alleged that very low energy levels are absorbed in the bodies of patients, which can lead to enhanced risk of radiation-based problems such as cancer. To address this problem, some medical imagers utilize filters to filter out the lowest energy photons. These filters do filter out the lower energies, but they also reduce the number of higher energy photons. Thus, the result is medical imagers that lack the needed intensity to form clear images.
Some medical imagers are termed multi-energy imagers, which image at two or more energies. By utilizing two energies, compositionally different materials in an image are more easily distinguished than when imaged with a single energy. Current multi-energy imaging systems form the images from different energy regimes by operating the x-ray source tube at different voltages, e.g., 80 kVp and 140 kVp. Then, in the simplest analysis, the images can be subtracted to produce an image formed predominantly from the higher energies, from 80 to 140 keV, but some energies below 80 keV are still present. Ideally comparing an image formed solely by 80 to 140 keV photons to one produced by energies below 80 keV would enable clear distinction between materials of different composition. However, in practice, energies below 80 keV are typically present in the “high-energy” image introducing significant difficulty and complexity into the resulting image analysis.
Some medical imagers are termed 4D imagers. Such imagers are often used to create cardiac images so that medical personnel can ascertain whether any heart-related issues or abnormalities, for example obstructed, or clogged, arteries, exist in a patient. The way these imagers work is the patient is placed within a tube that weighs many hundreds of pounds. Once the patient is properly positioned, the tube is rotated at a rapid angular velocity. One issue with such imaging is the short time required for a sharp image of the heart at rest—i.e., between beats. A healthy adult person may have a resting heart rate of 60 to 80 beats per minute (bpm). The heart rate accommodates a number of variables such as age, weight, height, and physical fitness. Less fit persons, and frankly the ones more likely to be utilizing such imagers, have a resting heart rate far in excess of 60 bpm, sometimes as high as 150 bpm or more. It has been found that due to the weight of the x-ray source, spinning the source at the required high speeds is quite difficult. Thus, obtaining high quality images of a resting heart is quite difficult in a large percentage of the population.
Certain therapeutic techniques in use utilize ionizing radiation to address a health issue. For example, to remediate prostate cancer, one therapeutic technique includes placing radioactive beads in the prostate to destroy the tumor. One problem with this technique is that the radiation from these radioactive beads is isotropic, resulting in irradiation of other areas, for example femurs, possibly leading to an enhanced risk of leukemia.
Other disadvantages occur in imaging techniques that use ionizing radiation outside the medical field. For example, current inspection of cargo typically includes imaging the cargo contents within the container itself. This is usually performed by placing the cargo container on a truck and directing the truck to a certain location between an x-ray source and a detector.
Certain current x-ray source configurations transmit diverging x-rays. Nonetheless, to be able to image an entire cargo container during a single pass, the x-ray source must be at a great distance from the cargo container, on the order of one-half a mile or so. Since the x rays that eventually strike the cargo container have diverged so much by the time they reach the cargo container, the x-ray flux density is extremely low, necessitating long exposure times, on the order of 20 minutes or longer. With between 100 and 1000 cargo containers offloaded daily at ports, such long imaging times are impractical for every container. Forming a smaller beam with 100 to 1000 times or greater flux density could enable scanned inspection of every container.
Imaging techniques used to image printed circuit boards (PCB) typically lack the requisite intensity to address PCBs with ever increasing layers. Further, imaging techniques used in inspection of industrial parts also suffers from a lack of needed intensity. Such imagers are used on an almost continuous basis and utilize x-ray tubes that are less powerful but with a greater service life. The lack of needed intensity results in a failure to see intricate details, such as cracks in turbine blades or inability to inspect every part, for example.
X-ray imaging techniques are desired to inspect, for example, subsea risers used to bring oil and/or natural gas up to the surface from undersea wells. Inspection is sometimes used to ascertain whether any cracks are forming in the risers. However, present x-ray tubes do not provide sufficient x-ray flux to make such imaging inspection practical. Industrial x-ray sources with sufficient energy, on the order of 500 kVp, and x-ray flux, weigh several hundred pounds and produce so little x-ray flux that the data acquisition time for imaging is on the order of tens of hours or longer. During that time, risers tend to move along with the wave movement offshore, inhibiting formation of clear images of the subsea risers.
X-rays have also been contemplated for use in providing and disrupting communications. For example, a collimated high-energy, high-intensity x-ray beam could be used to send information to aircraft miles above the earth with almost no loss of signal, whereas lower energy photons are scattered by particles in the atmosphere. However, as noted previously, no known portable x-ray sources provide the kind of intensity and collimation to make such a use practical.
Some x-ray sources that could provide the intensity and collimation but not at the high energies needed for some of the applications previously discussed are called x-ray lasers. Currently, the only type of x-ray laser that is intense enough is a free-electron laser, most of which require synchrotrons. Such lasers are impractical because the synchrotrons are huge (on the order of 3.5 kilometers in diameter) and cannot be moved to the location of the sample. Recent advances in miniaturizing synchrotrons have led to free-electron lasers that are on the size of two large rooms and produce the desired collimated x-ray beam with just barely sufficient intensity. However, demonstrated energies are less than needed for many applications. Furthermore, these miniaturized synchrotron x-ray lasers require a very powerful visible laser (approximately one gigawatt of power) to excite the gain medium to start the x-ray emission process. So, while technically these known miniaturized synchrotron x-ray lasers may be mobile, finding a one gigawatt power source is difficult. Even with such a power source, the imaging energy level is only about 20 keV.
Additionally, synchrotron and collisional x-ray lasers are single pass lasers, which means the path over which the photons travel and undergo stimulated emission must be very long in order to produce high intensity.
Traditional x-ray imaging provides a map of the absorptive properties of a sample. Visualizing the initial stages of carcinomas and other histological structures can be difficult due to minimal distinction—a few percent—between their absorptive properties and those of surrounding tissue. However, it has been demonstrated that the refractive index changes can be significant enough to enable visualization of some histological structures. X-ray phase-contrast imaging creates images based on these refractive index differences. This type of imaging relies on a spatially coherent x-ray beam, such as can be provided by an x-ray laser, to traverse a sample containing regions of differing refractive indices and be refracted by these areas. Upon refraction, these x rays undergo a phase shift and lose their initial coherence. When these “incoherent” photons interact with un-refracted or direct x rays, constructive and destructive interference patterns are produced that are reconstructed into very high-contrast images of boundaries within the sample. One problem with phase contrast microscopy is the much higher intensity of the direct x-ray beam in comparison to the refracted beam causing a very low signal to noise ratio in the interference pattern.
In dark-field microscopy the direct beam can be suppressed, improving the contrast of an image by using only the scattered x rays. This type of imaging, like phase contrast imaging, requires a coherent incident x-ray beam, such as can be provided by an x-ray laser. The major issues with both types of imaging is the long exposure times required due to the low intensity laboratory (non-synchrotron based) x-ray sources currently available.
Holographic x-ray images with nanometer-scale resolution can be made of objects measured in microns in times as brief as femtoseconds. X-ray holography could be the enabling tool for developing nanoscience and nanotechnology. However, this technique depends on the wave-like properties of the x rays and requires the use of x-ray lasers, of which only synchrotron-based ones currently exist. Thus both the creation and viewing of x-ray holograms can only be performed at synchrotrons, which makes this technique impractical for use in enabling, for example, the development of many nanotechnologies.
What is desired is an x-ray laser that addresses one or more of the aforementioned disadvantages.